This invention relates to a friability testing apparatus. In one application of the invention, the apparatus can be used to test the friability of diamond particles.
A device known as a "Friatester" is currently used to test the friability of diamond particles. This device includes a round cylindrical capsule which is closed at its ends and which accommodates a hard spherical ball. In use, diamond grit the friability of which is to be tested is introduced into the capsule. The capsule is reciprocated back and forth in the direction of its axis with the result that the ball is thrown from end to end inside the capsule. Particles of grit are impacted by the ball and sandwiched between the ball and the relevant end of the capsule at each stroke, with the result that they are crushed. After the device has been in operation in this way for a set number of cycles, the grit is subjected to screen testing and a friability index (F.I.) is computed from the mass of the unbroken particles as a percentage of the mass of the original particle charge. The F.I. computed in this way has become an industry standard and has value to purchasers of diamonds who wish to know how the diamonds will perform in industrial applications such as in saws or abrasives.
In the known "Friatester" the capsule containing the material whose friability is to be tested and the steel ball, is reciprocated by means of a motor-driven crankshaft and connecting rod arrangement. With this kind of drive it is not possible to control the vibrations accurately or to vary them to suit different materials or classes of materials. In addition, despite rigorous calibration, the mechanical nature of the "Friatester" renders it liable to mechanical faults, such as wear, which to repeatability of performance which is less than optimum.